<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>css-demo盒子</title>

    <style>
        .red {
            height: 100px;
            width: 100px;
            background-color: red;
        }
        .green {
            height: 100px;
            width: 100px;
            background-color: green;
        }
    </style>

</head>
<body>
    
    <div class="red"></div>
    <div class="green"></div>
    <div class="red"></div>

</body>
</html>
